The present invention relates generally to the treatment of osteoporosis and afflictions characterized by inadequate local or general bone mass, and specifically the use of impact loading of bone under a gravitational or mechanically-induced preload.
Osteoporosis is a pernicious disorder usually, but not exclusively, afflicting elderly women. The osteoporotic state can also be manifest by those who are confined to bed and even by astronauts who are in a weightless environment. Osteoporosis occurs through a decrease in bone mass which makes the afflicted bones more fragile and more susceptible to breaking.
The fractures resulting from osteoporosis can cause death, require extended hospital stays, and sometimes involve expensive and painful surgery. Health care costs for this condition approach ten billion dollars per year in the U.S. alone. In addition, osteoporosis severely diminishes the mobility and vitality of those affected with the disease.
The general population also feels the effects of this disease. Persons afflicted with osteoporosis must depend upon relatives and others for care, and everyone is affected by the health care costs and the use of hospital or nursing home facilities attributable to this affliction.
The reduction in bone mass from osteoporosis results when bone destruction outpaces bone formation. The balance between destruction and formation is affected by hormones, calcium intake, vitamin D and its metabolites, weight, smoking, alcohol consumption, exercise and many other factors too numerous to catalogue here.
To slow or reverse bone loss, doctors have focused their attention on estrogens, calcium, and exercise, used either together or individually. More recently, fluorides and thiazides have been tested as therapeutic agents, but none of these approaches has been successful in restoring a severely depleted skeletal bone mass to normal. In addition, many elderly individuals with advanced bone loss cannot participate in exercise programs due to poor reflexes, motor tone and balance, as well as stress pain and stress fractures.
Certain researchers have suggested an electrical intermediary in Wolff's law. Wolff's law states, in short, that bone adapts to the forces acting upon it. In other words, bone will increase in mass and remodel to relieve the applied stress.
Because bone is piezoelectric and electrokinetic, it generates an electrical signal in response to the applied force. That electrical signal then effects bone formation. This is explained in Bassett, "Effect of Force on Skeletal Tissues," Physiological Basis of Rehabilitation Medicine, Downey and Darling eds., 1st ed., W. B. Saunders Co. (1971). On the basis of Wolff's law and more recent investigations, two techniques have been developed for treatment of bone disorders. One involves mechanical forces and the other involves electrical forces.
One of the first and most complete investigations into the effect of mechanical loading on bone tissue was reported in Cochran et al., "Electromechanical Characteristics of Bone Under Physiologic Moisture Conditions," Clinical Orthopaedics 58: 249-270 (1968). In that article, both in vitro and in vivo measurements showed the electrical potentials developed due to bone deformation. The results of this and related work led to the use of electromagnetic stimulation to control bone tissue as reported in Bassett et al., "Augmentation of Bone Repair by inductively Coupled Electromagnetic Fields," Science, 184:575-77 (1974), and Bassett et al., "A Non-Operative Salvage of Surgically Resistant Pseudarthroses, and Non-Unions by Pulsing Electromagnetic Fields, A Preliminary Report," Clinical Orthopaedics, 184:128-143 (1977). Such work and research also led to the development of products for the stimulation of bone tissue electromagnetically. In addition, some work was carried over into the treatment of osteoporosis, as reported in Bassett et al., "Prevention of Disuse Osteoporosis in the Rat by Means of Pulsing Electromagnetic Fields," (in Brighton et al., Electrical Properties of Bone and Cartilage: Experimental Effects and Clinical Applications, 311-33, 1979); Cruess et al., "The Effect of Pulsing Electromagnetic Fields on Bone Metabolism in Experimental Disuse Osteoporosis," Clinical Orthopaedics, 173: 245-250 (1983); and Rubin et al., "Prevention of Osteoporosis by Pulsed Electromagnetic Fields: An in vivo animal model identifying an osteogenic power window," J. Bone Joint Surgery, 71A: 411-17, 1989.
The Cochran paper also suggested the possibility of a critical mechanical loading rate to generate maximal voltages. To this end, patients have been treated with axial compression exercises, as reported in Bassett '71, on pages 312-314. In general, however, this work has received less attention than the electromagnetic work.
Some interest in mechanical methods of controlling bone loss has continued. For example, the National Aeronautic and Space Administration funded a study whose purpose was to use impact loading on patients' heels to stimulate bone formation. Reference to this work was described in an abstract printed in the U.S.P.H.S. Professional Association, 11th Annual Meeting (May 26-29, 1976), and entitled "Modification of Negative Calcium Balance and Bone Mineral Loss During Bed Rest: Impact Loading." The abstract reported that impact loading, which was kept to 25 pounds, could slow down the loss of calcium and achieve other beneficial results.
More recently, two papers by Rubin and Lanyon have suggested that periodical strain rates and cycling patterns generate maximal osteogenic response in avian bones. In one of those papers, entitled "Regulation of Bone Formation by Applied Dynamic Loads," The Journal of Bone and Joint Surgery, 66-A(3): 397-492 (March 1984), an experiment demonstrated that cyclically loading the bones at 0.5 Hz caused bone formation, although repetition of more than 36 cycles did not seem to increase bone formation. The paper also suggested that an abnormal strain distribution caused an increase in bone mass. In a later paper by Rubin et al. entitled "Regulation of Bone Mass by Mechanical Strain Magnitude," Calcif. Tissue Int. 37:411-417 (1985), Rubin and Lanyon also showed a graded dose response subjected to 100 load cycles at 1 Hz, and showed a graded dose response relationship between peak strain and change in bone tissue mass.
These techniques of treating bone disorders with repetitive forces, however, did not preload the bone before applying the repetitive force.
U.S. Pat. No. 5,046,484 issued to Bassett et al. describes a clinically effective method and device for applying repetitive force to a patient who stands on a platform and is lifted and dropped according to parameters determined from various patient and treatment information. This method, however, requires a patient to be physically lifted and dropped, which causes balance problems and discomfort to some patients. Also, the method does not adapt easily to other bones. Furthermore, since the frequency component of the impact is derived from the equation for force, F=ma, as "m" mass increases, "a" acceleration must decrease to maintain "F" force within a practical range. Thus, individuals with large body mass cannot achieve appropriate frequency contents in their impacts because low velocity impacts. Since the individuals cannot be raised too high, impacts with higher frequency content are not achieved.
Therefore, it is an object of the present invention to devise an improved treatment for osteoporosis in humans which is both safe and effective and which does not require lifting and dropping a patient.
It is a further object of the present invention to preload the skeletal structure before applying a repetitive force.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.